Treatment of pain or instability associated with lower extremity misalignment may require surgical interventions, such as osteotomy. High tibial osteotomies are indicated by early, medial joint-space narrowing, by early arthritis in patients who have had previous medial meniscectomy, or following rupture of the anterior cruciate ligament in patients with pre-existing varus deformity, for example.
Two osteotomy methods are known in the art: the closed wedge method, and the open wedge method. In the closed wedge method, removal of a bone wedge creates an angled gap in the bone. Part of the bone is left as a hinge at the apex of the angle. The hinge allows the gap to narrow, and the bone material on either side of the closed gap joins together. In the open wedge method, a cut is made across the bone. Part of the bone is left as a hinge, as in the closed wedge method. In contrast to the closed wedge method, however, the hinge allows the cut gap to open. The open wedge is filled with graft material. The two osteotomy methods are performed on opposite sides of the bone to give equivalent results. For example, when a given deformity would be corrected by performing the open wedge procedure on the medial side of a bone, an equivalent closed wedge correction would be performed laterally.
The closed wedge method is the current standard, although several disadvantages are associated with this technique. The most significant disadvantages of the closed wedge method are: (1) disruption of the tibial-femoral joint; (2) possible damage to neurovascular structures; and (3) disruption of the medial cortex, resulting in instability and nonunion between the upper and lower bone because of possible soft tissue interference. It is also difficult to compute the correct amount of bone to remove and, therefore, several extra cuts may be required.
The open wedge method avoids or mitigates many of the disadvantages associated with the closed wedge method. Additionally, the medial, open-wedge high tibial osteotomy has the following advantages over the closed, lateral-wedge high tibial osteotomy: (1) speed; (2) simplicity; (3) ability to quickly change angle at any time during the procedure; and (4) no requirement for fibular osteotomy. Open wedge osteotomy procedures are disclosed, for example, in U.S. Pat. Nos. 5,620,448 and 5,749,875, both of which are assigned to Arthrex, Inc. and incorporated herein by reference.
Because the open wedge method leaves a gap in the bone, a brace is necessary to fix the portions on either side of the gap relative to each other and bear weight until new bone grows to fill the gap. Conventionally, the brace is a bone plate formed of stainless steel or titanium. The bone plate is typically affixed to the bone portions on either side of the gap with steel or titanium screws inserted through pre-formed screw holes in the bone plate. One such bone plate is disclosed in U.S. Pat. No. 5,749,875 referenced above.
Because conventional bone plates are formed of a hard metallic material (e.g., stainless steel or titanium), they offer sufficient strength but the angle at which screws must be inserted is fixed, either by threading or by providing a tapered portion on the interior of the screw holes. This is disadvantageous because it may prevent a surgeon from adjusting the insertion angle of the fixation screws to better accommodate the curvature of a patient's bone. Thus, there is a need in the art for a bone plate that can accommodate fixation screws inserted at different angles.